1. Field of the Invention.
This invention relates to the procedure for the implantation of intraocular lenses, and particularly to a method and means for effecting such implantation procedure while minimizing the likelihood of damage to the corneal endothelium and iris.
2. Description of the Prior Art
A preliminary patentability and novelty search of the prior patent art pertaining to the instant invention has revealed the existence of the following U.S. Pat. Nos.:
______________________________________ 4,600,003 4,600,004 4,657,011 4,693,716 4,701,181 4,769,034 ______________________________________
U.S. Pat. Nos. 4,600,003 and 4,600,004 relate to a tool for inserting an intraocular lens through an incision made for that purpose. The lens is loaded onto the tool, the tool is then inserted through the incision, and the lens is then pushed off the tool and into position within the eye. A major purpose of the tool is to retain the haptics in a collapsed condition during the insertion process. It is stated in these patents that the tool may be fabricated from any of the common plastics currently in use.
U.S. Pat. No. 4,657,011 relates to a guide device for assisting the insertion of an intraocular lens into the capsular bag from which the natural lens has been aspirated. The guide, as stated in the patent in column 3, lines 17 through 20, inclusive, is preferably made from a thin, flexible material which will not interact with the eye, for example, thin metal like stainless steel or plastic like polyethylene or polypropylene. One end of the strip, which has a distal end portion bent over upon the remainder of the strip, is first inserted into the eye through an appropriate incision, and then the lens to be implanted is caused to slide along the guide until it is deposited within the capsular bag. The guide is then withdrawn.
U.S. Pat. No. 4,693,716 relates to a multi-part lens structure and does not appear to have any relevance with respect to the instant invention.
U.S. Pat. No. 4,701,181 relates to a specific lens design rather than to a device for protecting the corneal endothelium or the iris tissue. The stated purpose of the design is to enable utilization of polymethylmethacrylate (PMMA) for the haptics in place of haptics formed from prolene (polypropylene) which are stated as subject to degradation in the eye. Thus, the lens structure disclosed by this patent includes a lens formed from PMMA and haptics formed from PMMA, a material that is particularly susceptible of causing damage to the corneal endothelium if the PMMA comes into contact with it. Nothing in this patent suggests a means of preventing such damaging contact of the lens or haptics with the corneal endothelium or the iris tissue.
Until relatively recent years, lenses were implanted in the anterior chamber of the eye, and surgical techniques were developed to facilitate insertion of the lenses and suspension of the lenses on the iris. Very early, it was recognized that PMMA (polymethylmethacrylate) was a desirable material for use as an optic because of its optical clarity and the ease with which it can be milled and lathed. As early as 1976 however it was revealed in an article by Kaufman and Katz, published in Invest Ophthalmol Visual Science, volume 15, pages 996-1000, that even a momentary contact of the PMMA lens surface and the corneal endothelium causes a physical adhesion of endothelium cells to the lens, the cells being torn from the endothelium when the surfaces are separated, causing extensive cell damage or cell death. An article by Levy and Roth, published in OPHTH, Vol. 86, pages 219-227, Feb. 1979 explains an experiment using cat eyes in which a new surgical technique is described which implements a sheet of Polymacon cut to the size of the anterior chamber and draped over the anterior surface of the lens so that during insertion the corneal endothelium is protected from contact with the intraocular lens. As stated in the article, a significant reduction in endothelium cell loss occurs when the corneal endothelium is protected against contact with the intraocular lens. Numerous other articles and experiments confirm this early finding. It is surprising therefore that more prior art references have not been found disclosing structural implementation of the corneal endothelium protection concept revealed in the scientific literature.
In another article entitled Corneal Endothelium Loss With New Intraocular Lenses, published in 1984 in the American Journal of Ophthalmology, volume 98, pages 137-165, there is described a comparison of the damage that results to the corneal endothelium by no contact (0.4%); by contact with uncoated methylmethacrylate (62%); by contact with hydrogel intraocular lenses (3.6%) which is said to be not significantly different from the "no contact" degree of damage; by contact with methylmethacrylate lenses coated with sodium hyaluronate (27.4%); and methylmethacrylate lenses coated with methylcellulose (57.2%).
This article goes on to discuss that of the approximately 600,000 patients (in 1984) who undergo cataract operations each year in the United States alone, about 70% of them receive an intraocular lens implant. It goes on to say that the most serious late complication of implant surgery is intractable corneal edema leading to loss of corneal transparency which may not appear until three to five years after implant. It attributes corneal decompensation largely to the result of profound loss of endothelial cells during surgery by contact of the methylmethacrylate lens with the corneal endothelium. Even after implantation, it is said that there is a progressive loss of endothelial cells which may be the result of chronic uveitis.
Recognition of the danger of touching the corneal endothelium is indicated by the fact that for about the last eight years, ophthalmologists have relied on viscoelastic gels that are injected into the anterior chamber of the eye to form a barrier tending to prevent inadvertent contact of the PMMA lens with the corneal endothelium. Such viscoelastic gels are costly, and pose the risk of postoperative complications such as increased intraocular pressure and inflammation. Because of these risks, many surgeons now aspirate the gel out of the eye prior to wound closure in an effort to minimize such risks.
In view of these findings, particularly since PMMA intraocular lenses appear to be the least costly and the type that are presently most prescribed and implanted, it is even more surprising that a greater effort has not been expended in conceiving and manufacturing protective devices, apart from injected gels, to be used by the surgeon during the implantation procedure. One justification that might be offered is that ophthalmologists are confident they can implant a lens without touching the corneal endothelium, and the use of a protective device constitutes an implied derogation of their ability. Nevertheless, in view of the severe and lasting damage that can occur by the mere touching of the corneal endothelium with the surface of the PMMA intraocular lens, it is submitted that the protective device forming the subject matter of the present invention is sorely needed and will find immediate acceptance by ophthalmologists.
Accordingly, one of the objects of the present invention is the provision of a method for protecting the corneal endothelium and/or iris tissue during the implantation procedure without unduly complicating the procedure, and perhaps even simplifying the procedure by eliminating some of the anxiety that a surgeon must experience in an effort to avoid contacting the corneal endothelium with the intraocular lens.
Another important object of the present invention is the provision of a protective device that may be applied to an intraocular lens prior to insertion into the eye for the purpose of forming a protective boundary between the lens structure and the corneal endothelium and/or the iris tissue.
Still another object of the invention is the provision of a protective device that is biocompatible with the corneal endothelium and which may be applied to the intraocular lens in such a manner that the insertion force applied to the lens acts to ensure that the protective device remains on the lens until it is properly positioned within the eye.
A still further object of the invention is the provision of a protective device for application to an intraocular lens, particularly a lens fabricated from PMMA, which is easily removed from the eye following insertion of the lens.
Still another object of the invention is the provision of a protective device that is fabricated from hydrophilic material and which may be applied to the lens so as to completely cover either the anterior surface thereof, the posterior surface thereof, or both anterior and posterior surfaces.
Yet another object of the invention is the provision of a protective device fabricated from hydrophilic material that contains sufficient water when applied to the lens that the protective device has a natural affinity for the lens, causing the hydrated protective device to adhere adequately to the lens so as to minimize inadvertent displacement of the protective device on the lens.
Still another object of the invention is the provision of a protective device for application to an intraocular lens which forms a temporary boundary between the lens body and surrounding tissue, but which nevertheless permits adjustment of the position of the lens body so as to enable alignment of the optic axis of the lens with the optic axis of the eye.
A still further object of the invention is the provision of a protective device for application to an intravocular lens according to the foregoing objects which is colored to provide visual differentiation from the intraocular lens to which it is applied.
The invention possesses other objects and features of advantage, some of which, with the foregoing, will be apparent from the following description and the drawings. It is to be understood however that the invention is not limited to the embodiment illustrated and described since it may be embodied in various forms within the scope of the appended claims.